System and method for the early detection of cellular telephone piracy

ABSTRACT

A method and system for early piracy detection in a cellular telecommunications network is disclosed. When in idle mode, a network subscriber Mobile Station (MS) transmits a Current Location Identifier message (CLID) on a pseudo-random basis. The CLID, which contains MS identifying information, is picked up by the network and relayed to the Mobile Switching Center (MSC) covering the area in which the MS is currently located. When it receives the CLID, the MSC generates an MS-CLID message containing the CLID and the identifier of the nodes through which it has passed, including that of the MSC itself. The MS-CLID message is then sent to the system Home Location Register (HLR), which compares the MS identification and location information to that stored in its database. The system generates a piracy alarm when the comparison determines that another caller using the same identity is currently active or that a call being initiated is originating from a location distant to the last reported location of the legitimate MS, allowing the system operator to take action prior to the loss of inordinate amounts of air time.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates to cellular telephone networks and, inparticular, to a system and method for the early detection of cellularpiracy, more particularly to a system and method where the systemoperator can take action to stop unauthorized system use upon activationof a piracy alarm signal.

2. Description of the Related Art

The evolution of wireless communication over the past century, sinceGuglielmo Marconi's 1897 demonstration of radio's ability to providecontinuous contact with ships sailing the English Channel, has beenremarkable. Since Marconi's discovery, new wireline and wirelesscommunication methods, services and standards have been adopted bypeople throughout the world. This evolution has been accelerating,particularly over the last ten years, during which the mobile radiocommunications industry has grown by orders of magnitude, fueled bynumerous technological advances that have made portable radio equipmentsmaller, cheaper and more reliable. The exponential growth of mobiletelephony will continue to rise in the coming decades as well, as thiswireless network interacts with and eventually overtakes the existingwireline networks.

In order to promote compatibility of the equipment and operations ofvarious Public Land Mobile Networks (PLMN), air-interface standards havebeen developed and are currently being implemented. In North America,the most widely used standard protocol is the Advanced Mobile PhoneSystem (AMPS), which is now being supplemented by a digital version(D-AMPS). Another such standard is the Global System for MobileCommunications (GSM), used throughout Europe and in some parts of theUnited States. In each standard, PLMN operators set up permanentequipment to cover a given geographical area and enlist mobilesubscribers. The subscriber is billed by the operator for cellularservice, generally paying a base charge in addition to a variable chargebased on the subscriber's use of the system.

Unfortunately, along with the popularity of cellular telephone has comecellular piracy. A pirate scans the air interface for cellular phonesinitiating a connection with the PLMN, exploiting initializationprocedures. To begin a call, a cellular Mobile Station (MS) firsttransmits a signal over the air interface that includes unique MSidentifying information. This identification information indicates thataccess to the cellular system is being requested by a system subscriber,and is used by the PLMN for, among other things, billing the subscriberfor the call. An eavesdropping pirate who intercepts this initialtransmission can then replicate the signal and construct a "clone," thatis, an MS that transmits identical identification information.

When the clone thereafter initiates a call using the subscriber'sidentity, the PLMN cannot distinguish between the pirate caller and thelegitimate subscriber; system access will be granted to both. Thegeographical location of the clone is no help in making any distinction,since the subscriber can "roam," that is, make and receive calls whilelocated outside its home service area. Of course, the legitimatesubscriber is billed for all the usage. Pirates often operate a singleclone for approximately one month, after which time the subscriber willlikely receive and protest an inordinately high cellular service bill.Although steps can then be taken to avoid further unauthorized use, thePLMN operator generally bears the cost of the calls already made by theclone, resulting in the loss of thousands of dollars of air-timerevenue. This problem is most acute in PLMNs operating under theAMPS/D-AMPS protocols, which lack the techniques available, for example,as in the GSM environment.

At present, enforcement against pirates is difficult at best. Clones arequickly abandoned after short periods of high use, after which thepirate acquires another cloned identity. Accordingly, there exists aneed for a way to detect clone use earlier so that unauthorized use maybe stopped and an attempt made to track down the pirate before largeamounts of air time are stolen.

SUMMARY OF THE INVENTION

To address that foregoing and other problems, the present inventionproposes a system and method for initiating a clone alarm immediatelywhen a potential piracy condition occurs. In a preferred embodiment, anidle Mobile Station (MS) belonging to a legitimate subscriber in acellular telephone network, when not connected, transmits a CurrentLocation Identifier message (CLID) on a pseudo-random basis. The CLIDcontains MS identification information. The CLID is picked up by theBase Transceiver Station (BTS) and transmitted through the Base StationController (BSC) to a Message Switching Center (MSC). The MSC assemblesan MS Location Identifier message (MS-CLID) containing the CLID andidentity of each node through which the CLID has passed. The MSC thentransfers the MS-CLID to the system Home Location Register (HLR), whichchecks to see if an entity appearing identical to the CLID-transmittingMS is currently active. If so, a piracy condition exists and a clonealarm is transmitted to the system operator. Preferably, the frequencyof the pseudo-random CLID transmissions can be varied by the systemaccording to the current geographical location of the MS. More frequenttransmissions could be made in areas known to have extensive piracyoperations. In another embodiment, the identity check is performed in aseparate authentication/privacy register (APR) to conserve HLRresources.

In yet another embodiment, whenever the HLR receives a registration fromthe MS or an MS-CLID, it updates its CLID database to reflect the new MSlocation information. Preferably, the location information stored in theHLR database will include the last-received MS-CLID. The HLR alsoinitiates a transmission back to the MS so that the MS can store innon-volatile memory the MS-CLID stored in the HLR database. This storedMS-CLID is included by the MS when it next transmits a CLID. In thisembodiment, when the HLR next receives an MS-CLID, then in addition tochecking for active clones, it also verifies that the new MS-CLIDcontains within it the old MS-CLID previously returned to the MS. Ifnot, a potential piracy condition exists because a clone is trying toemulate the MS by transmitting a CLID, and a clone alarm is transmittedto the system operator.

In yet another embodiment, the HLR also maintains information regardingthe pseudo-random generation pattern that determines when an MS willtransmit a CLID. Although an MS may fail to transmit a CLID at the nextinterval, for example because it is connected at the time, it is in thisembodiment configured to transmit at an expected time. Upon receipt ofan MS-CLID transmission, the HLR, in addition or as an alternative toother comparisons, verifies that the CLID was sent at an appropriatetime. If not, a potential piracy condition exists and a clone alarm istransmitted to the system operator.

Upon receiving a clone alarm, the system operator can choose fromseveral possible courses of action. For example, the operator couldattempt to ascertain the suspected pirate's location, or could interruptthe suspected pirate's call to determine whether it is being placed by alegitimate subscriber. Short of investigating each alarm, the eventcould simply be noted and the suspected pirate's location recorded forfuture use. Tracking could then be initiated after a number of alarmshave been received for the same MS. In any event, the system operatorwill have notice of a piracy situation long before a subscribercomplains of an erroneous cellular telephone bill.

A more complete appreciation of the present invention and the scopethereof can be obtained from the accompanying drawings which are brieflydescribed below, the following detailed description of thepresently-preferred embodiments of the invention, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the method and apparatus of the presentinvention may be obtained by reference to the following detaileddescription when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a block diagram of a telecommunications system according tothe present invention;

FIG. 2 is a block diagram of a telecommunications system illustratingthe routing of a CLID/MS-CLID message according to the presentinvention;

FIG. 3 is a flow chart illustrating how the system uses the MS-CLID inthe piracy detection process according to one embodiment of the presentinvention;

FIG. 4 is a block diagram illustrating the routing of CLID/MS-CLID andlast reported location messages in accordance with the presentinvention; and

FIG. 5 is a flow chart illustrating how the system uses the MS-CLID inthe piracy detection process in accordance with an alternativeembodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

With reference to FIG. 1 of the drawings, there is illustrated PublicLand Mobile Network (PLMN) 10, such as cellular network, which in turnis composed of a plurality of areas 12, each having a Mobile SwitchingCenter (MSC) 14 and integrated Visitor Location Register (VLR) 16therein. The MSC/VLR areas 12, in turn, include a plurality of LocationAreas (LA) 18. An LA 18 is that part of a given MSC/VLR area 12 in whicha Mobile Station (MS) 20 may move freely without having to send updatelocation information to the Home Location Register (HLR) 26, describedbelow. Preferably, the MSCs are connected to the HLR via a SignalingSystem #7 (SS7) network.

Each Location Area 18 is divided into a number of cells 23. MS 20 is thephysical equipment, e.g., a car phone or other portable phone, used bymobile subscribers to communicate with the cellular network 10. A BaseTransceiver Station (BTS) 24 is the physical equipment, illustrated forsimplicity as a radio tower, that provides radio coverage to thegeographical area of the cell 23 in which to handle radio traffic to andfrom the MS 20. One or more BTSs are controlled by a Base StationController (BSC) 25, and one or more BSCs may be governed by a singleMSC 14.

With further reference to FIG. 1, the PLMN Service Area or cellularnetwork 10 includes an HLR 26, which is a database maintaining allsubscriber information, e.g., user profiles, current location androuting information, and other administrative information. The HLR 26itself may be co-located with a given MSC 14, may be an integral part ofan MSC 14, or may service multiple MSCs 14; the latter configurationbeing illustrated in FIG. 1. In accordance with the present invention,the BTS, BSC, MSCs, VLRs and HLR together make up a network securitysystem 28.

The MS's current location stored in the HLR 26 database is in the firstinstance determined through a process called registration. Inregistration, MS 20 transmits a registration request message on acontrol channel to the cell-controlling BTS 24. The BTS 24 in turndirects the message through its associated BSC 25 to MSC 14 (updatingVLR 16, if necessary, such as when MS 20 is roaming), and then to HLR26. Registration typically occurs when MS 20 is powered-up, when itroams from one LA 18 to another, or at other predetermined times, suchas when a call is placed. The MS 20 location information stored on theHLR 26 is used (in conjunction with VLR 16, if necessary), for example,when a call to the MS 20 is attempted.

As discussed, to steal air time from the cellular service provider, apirate mimics the registration process when placing a call. By scanningthe air interface, the pirate picks up a registration message andconstructs a clone capable of sending an identical transmission. Sincecalls made from the clone will be indistinguishable from legitimatecalls, both will be billed to the subscriber. The subscriber and thesystem operator will generally be unaware that cloning has occurreduntil a bill charging for call made by the clone is generated. Earlypiracy detection can be accomplished, however, by further cooperationbetween the MS 20 and network security system 28.

In a preferred embodiment of the present invention, during an idleperiod the MS 20 generates a signal, such as a Short Message Service(SMS)/page signal, called a Current Location Identification message(CLID). The CLID contains identification information unique to MS 20.With reference now to FIG. 2, there is shown a block diagram of atelecommunications system illustrating the routing of a CLID between theMS 20 and the HLR 26 according to the present invention. As withregistration, the MS 20 first transmits the CLID over a control channelon the air interface to a cell-controlling BTS 24. The BTS 24 thenforwards the CLID to its BSC 25. From BSC 25, the CLID is sent to MSC14. The MSC 14 determines the exact logical path back to MS 20,including the MSC 14 identifier, the VLR 16 identifier (if any)associated with MSC 14, the BSC identifier, and the BTS identifier. TheMSC 14 then contacts HLR 26 and transmits a Mobile Station-CurrentLocation Identifier message (MS-CLID), which includes the CLID and theaforementioned logical path identifiers. Preferably, the MS-CLIDincludes the CLID transmitted by the MS and the identifiers of the BTS,BSC, MSC, and (if applicable) VLR. It is not essential, however, thatthe MS-CLID comprise all of these elements, or that it exclude others,but it is preferable that the MS-CLID transmitted to the HLR 26 containas precise location and signal-path information as is possible.Preferably, the CLID and MS-CLID transmissions are accomplished via aSignaling System #7 (SS7) Transaction Capabilities Application Part(TCAP) inquiry.

Reference is now made to FIG. 3, which is a flow chart illustrating howthe HLR 26 uses the MS-CLID. As heretofore discussed, in accordance withthe present invention the CLID, and hence the MS-CLID, contains withinit a unique identifier associated with the MS 20 that originated theCLID transmission. The HLR 26 (shown in FIG. 2) contains the applicationthat processes the MS-CLID signal. Upon receipt of the MS-CLID, step301, the HLR 26, at step 305, initiates another TCAP inquiry todetermine whether any other entity using the same unique MS identifieris active. Since the CLID is only transmitted by an idle MS, if any VLR16 responds affirmatively, step 310, a clone alarm is generated by theHLR 26 at step 315. Alternately, activity status information could becontinually updated by the VLRs 16 and stored in the HLR 26 database, inwhich case the simultaneous activity determination could be made withoutfirst making a TCAP inquiry (not shown). If, on the other hand, no VLR16 responds affirmatively, step 320, then the HLR drops the MS-CLIDmessage without generating an alarm, step 330.

In another embodiment, the HLR 26 determines at step 340 the logicalpath back to the clone, that is, the entity active when the MS-CLID wasreceived. The time of the alarm, the MS 20 location, and the clonelocation are then recorded for future reference, step 350.

Although the CLID can be sent any time the MS 20 is idle, it ispreferably initiated on a pseudo-random basis. This prevents a piratefrom evading detection simply by placing calls during intervals when noCLID transmission is expected. The frequency of the pseudo-randomtransmissions is determined by an algorithm and seed resident in the MS20. As these are never transmitted by the MS, it is not possible for apirate to accurately predict the time of the next CLID transmission.

In a particularly preferred embodiment (not shown in FIG. 3) , when theHLR 26 is notified that the MS is operating in an area with high piracyactivity, as determined by the system operator based on past experience,the HLR 26 requests that the MSC 14 of the area in which MS 20 iscurrently operating generate a new seed and transmit it to the MS 20 Thenew seed, in combination with the algorithm resident on the MS 20,results in CLID transmissions occurring at more frequent intervals. Whenthe MS leaves the area, CLID frequency is reduced in the same way.

In yet another embodiment (not shown in FIG. 3), a powered-down MS 20will be automatically powered-up at the appropriate time to send a CLIDmessage and then powered down again to conserve battery power. Thisfeature could be manually disabled when CLID transmission should notoccur, such as during a plane flight.

In yet another embodiment, the simultaneous activity check is notperformed by the HLR 26 itself, but by a separate Authentication/PrivacyRegister (APR) 27 (shown in FIG. 2), which has access to the HLR 26database. In this embodiment, the HLR resources are not diverted to thisseparate operation, except for acting as an intermediary messagetransfer node.

The amount of information contained in the piracy alarm message, or thatis recorded, varies at the discretion of the system operator. It ispreferable that the operator be notified of the cause of the clonealarm, and of the location of the clone as near as can be determined.Upon receiving a piracy alarm, the system operator could attempt to moreprecisely identify the clone's location by standard techniques, such assignal loop-back time/triangulation.

Reference is now made to FIG. 4, which is a block diagram illustratinganother embodiment of the present invention. In this embodiment,increased protection is obtained, although at a higher burden on systemresources. Referred to here as "heavyweight" protection, this embodimentprovides increased piracy detection in instances when the clone is notactive simultaneously with a CLID transmission. To achieve this result,MS 20 has a non-volatile memory address (LM) 21 where the lastcalculated MS-CLID is stored. In heavyweight configuration, the CLID andMS-CLID are transmitted as aforedescribed in reference to FIG. 2, but inaddition, the MS-CLID, preferably including the identifier of the BST,the BSC, and the MSC, along the path traveled by the CLID orregistration message, is returned via the same path to MS 20 where it isstored in the LM 21. Generally, when LM 21 stores an MS-CLID received byMS 20, any previously stored information is deleted. It is foreseen,however, that multiple MS-CLIDs could be stored and applied to providingadditional protection in accordance with the present invention. Whenevera CLID is generated by MS 20, it includes the last-received MS-CLIDstored in LM 21 (and, if desired, additional historical information).

Reference is now made to FIG. 5, which is a flow chart illustrating theheavyweight operation of HLR 26 in conjunction with an associated APR27. In this embodiment, when the HLR 26 receives an MS-CLID (step 301),it generates a TCAP query containing the MS-CLID and transmits it to APR27 (step 500). The APR 27 then performs a number of checks (which arehereinafter described in a preferred sequence, but which can beperformed in any order without deviating from the spirit of theinvention).

First, the APR 27 performs the aforementioned simultaneous activitycheck. Upon receipt of an MS-CLID, APR 27 determines at step 505 whetherany other entity using the same unique MS identifier is active. For thepurposes of this embodiment, it is unimportant whether informationconcerning MS activity status is continually updated in the APR 27 (orHLR 26) database, or whether a separate query must be made to determinethe information whenever an MS-CLID is received. As aforedescribed withreference to FIG. 3, if any VLR 16 responds affirmatively, step 510, apiracy condition exists and a clone alarm is generated at step 315. If,on the other hand, no affirmative response is received, step 320, thenthe other checks are nonetheless performed, preferably beginning withthe timing check (step 530).

The APR 27, which has stored in its database the pseudo-random CLIDinterval algorithm and seed used by MS 20, verifies at step 530 that theCLID was generated at an expected time. Although a pirate may interceptand emulate a CLID, it will not have the algorithm and seed possessed byMS 20 and APR 27. Any CLID transmitted by a clone will therefore almostcertainly occur at the wrong interval. If APR 27 determines at step 530that this has occurred (step 535), a piracy condition exists and a clonealarm is generated (step 315).

In addition, because the previously received MS-CLID was both stored andreturned to the MS 20, the APR 27 database (or, alternatively the HLR 26database) and the LM 21 both hold in storage the same MS-CLID. When theMS 20 next transmits a CLID message, it includes this previous locationinformation ("old MS-CLID"), which is in turn included in the "newMS-CLID" calculated by MSC 14 and transmitted to HLR 26 and APR 27. Ifstep 530 confirms that the CLID was generated at an expected interval(step 540), this old MS-CLID, now contained in the newly receivedMS-CLID, is compared in step 550 to the old MS-CLID stored in the HLR 26or APR 27 database. If the old MS-CLIDs do not match, step 555, apossible piracy situation exists or has occurred and a piracy alarm issent to the system operator, step 315. Of course, if no previous MS-CLIDwas stored in a system database and transmitted to MS 20 for storage inLM 21, then a "match" will still occur. If a match occurs, step 560, theHLR 26 or APR 27 again updates its database to reflect the newlyreceived MS-CLID, step 565, and notifies the MSC 14 (step 570), whichtransmits the new MS-CLID to the MS 20, where it replaces the previouslystored information in LM 21 (step 575).

Although a specific process is illustrated in FIG. 5, it should be notedthat it is not critical to the invention how the data storage, dataprocessing, or alarm functions are allocated between the HLR 26 and theAPR 27. Even in the heavyweight embodiment, all functions could beperformed by the HLR 26 and it is not necessary in that case that an APR27 is present. As with the aforedescribed lightweight mode, if the HLR26 (or APR 27) is updated when an MS 20 becomes active or inactive, aseparate TCAP query to determine this status (upon receipt of anMS-CLID) can be eliminated. Also, as aforedescribed with reference toFIG. 3, if desired, the system could also or in the alternativedetermine the clone's location, step 340, and generate a clone report(step 350).

Although an embodiment of the method and apparatus of the presentinvention has been illustrated in the accompanying drawings anddescribed in the foregoing detailed description, it will be understoodthat the invention is not limited to the embodiment disclosed, but iscapable of numerous rearrangements, modifications and substitutionswithout departing from the spirit of the invention as set forth anddefined by the following claims.

The previous description is of a preferred embodiment for implementingthe scope of the invention should not necessarily be limited by thisdescription. The scope of the present invention is instead defined bythe following claims.

What is claimed is:
 1. A method for detecting piracy of a mobile stationwithin a cellular telecommunications system, said method comprising thesteps of:maintaining, within a database of said telecommunicationssystem, an activity flag associated with said mobile station, saidactivity flag being set when said mobile station is active;transmitting, automatically by said mobile station, an identificationsignal a plurality of times while said mobile station is idle, whereinsaid mobile station, if in a powered-off condition at the time saididentification signal is scheduled for transmission, automaticallypowers-on for a period at least long enough for said transmission tooccur; determining, after at least one of said identification signaltransmissions, whether said activity flag for said idle mobile stationis active; and generating an alarm signal if said activity flag for saididle mobile station is active.
 2. The method of claim 1, wherein saididentification signal is transmitted by said idle mobile station atpseudo-randomly spaced intervals.
 3. The method of claim 2, wherein saidpseudo-random intervals are determined using an algorithm that is storedin both said mobile station and said database, and further comprisingthe steps of:determining, after at least one of said identificationsignal transmissions, whether said at least one identification signaltransmission occurred at a time predictable by said algorithm; andgenerating an alarm signal if said at least one identification signaltransmission was not sent at a time predictable by said algorithm. 4.The method of claim 2, further comprising the step of varying thefrequency of said pseudo-random transmissions by a control signal sentto said mobile station.
 5. The method of claim 4, wherein said varyingstep varies said frequency of said pseudo-random transmissions based onthe areas in which said mobile station had been recently operating. 6.The method of claim 1, further comprising the steps of:maintaining,within a database of said telecommunications system, a last-reportedlocation of said mobile station; determining, after said at least oneidentification signal transmission, a current location of said mobilestation within said telecommunicating system; comparing said currentlocation of said mobile station after said identification signaltransmission to said last-reported location; and generating an alarmsignal if said current location of said mobile station is different fromsaid last reported location.
 7. The method of claim 1, furthercomprising the steps of:determining, after said at least oneidentification signal transmission, the identification signal path,wherein said identification signal path includes an identifiercorresponding to at least one of the nodes of said telecommunicationsystem through which said identification signal has been most recentlytransmitted; maintaining, within a database of said telecommunicationssystem, said identification signal path; updating, after said comparisonstep, said last reported location of said mobile station within saidlocation database to the current location; transmitting, to said mobilestation, said identification signal path; storing, within a memory ofsaid mobile station, said identification signal path as it is received;transmitting, from said mobile station, a second identification signal,wherein said second identification signal includes said updatedidentification signal path last received by said mobile station;comparing said identification signal path within said secondidentification signal to said identification path in said database ofsaid telecommunications system; and generating an alarm signal if saididentification signal path within said second identification signal isdifferent from said identification signal path in said database of saidtelecommunications network.
 8. The method of claim 1, wherein saiddatabase of said telecommunications system is located within a homelocation register of said telecommunications system.
 9. The method ofclaim 1, wherein said determining step is performed within anauthentication register in communication with the home location registerof said telecommunications network.
 10. The method of claim 1, whereinsaid activity flag indicates whether the mobile station is active basedon a query to visitor location registers in communication with saidtelecommunications system.
 11. The method of claim 10, wherein saidquery is made after at least one of said identification signaltransmissions.
 12. The method of claim 1, wherein said activity flag isset based on a notification provided by visitor location registers whensaid mobile station becomes voice-active or inactive.
 13. The method ofclaim 1, additionally comprising the step of determining a specific areain which a suspect clone is operating.
 14. The method of claim 13,wherein said suspected operating area is determined by a signalloop-back time triangulation process.
 15. The method of claim 1, whereinsaid alarm signal causes a piracy report to be generated.
 16. A methodfor detecting piracy in a telecommunications system, said methodcomprising the steps of:maintaining, within a home location register, alocation database containing a plurality of locations of a correspondingplurality of active mobile stations associated with thetelecommunications system; transmitting, from a given one of said mobilestations, a current location identifier, said current locationidentifier corresponding to said given mobile station; relaying saidcurrent location identifier of said given mobile station to said homelocation register; determining, within said home location register uponreceipt of said current location identifier, whether an active mobilestation identifier, for at least one of said locations in said locationdatabase of said active mobile stations, matches said current locationidentifier; generating an alarm if, in said step of determining, saidcurrent location identifier matches said active mobile stationidentifier; determining the location of said given mobile stationtransmitting said current location identifier; updating said locationdatabase in the home location register to said current locationidentifier location; transmitting said current location identifierlocation to said given mobile station, said given mobile station storingsaid current location identifier location in a memory therein;transmitting from said given mobile station, a second current locationidentifier, said second current location identifier including saidstored current location identifier; comparing said stored currentlocation identifier in said second current location identifier to saidcurrent location identifier for said given mobile station in saidlocation database; and generating said alarm if the stored currentlocation identifier within said second current location identificationdoes not match said current location identifier for said given mobilestation in said location database of said home location register. 17.The method of claim 16, further comprising the step of:varying thefrequency of said transmission of said current location identifier basedon the areas in which said mobile station had been recently operating.18. The method of claim 16, further comprising the step of determiningthe location of a suspected clone whenever said alarm is generated. 19.The method of claim 18, wherein said alarm caused a piracy report to begenerated.
 20. The method of claim 16, further comprising the stepsof:counting the number of current location identifiers transmitted bysaid given mobile station within a predetermined period; and alertingthe system operator if the number of transmissions counted in saidcounting step exceeds a predetermined threshold.
 21. A cellulartelecommunications system for detecting piracy of a mobile station, saidsystem comprising:a home location register having a location databasecontaining the last reported location of a plurality of mobile stationsassociated with said home location register; a signal generator in atleast one of said mobile stations for sending respective identificationmessages to said home location register said signal generator varyingthe frequency of transmission of said respective identification messagesbased on the areas in which said mobile station had been recentlyoperating; determining means for determining if said identifiercorresponding to a given one of said mobile stations matches theidentifier corresponding to at least one other active mobile stationsending said respective identification messages; and an alarm generatorfor generating an alarm if said given one mobile station identifiermatches said other active mobile station identifier.
 22. The system ofclaim 21, wherein said home location register determines the currentlocation of said given mobile station and transmits said currentlocation to said mobile station, and further comprising a storagelocation in said mobile station for storing location information sent toit from said home location register.
 23. A method for detecting piracyof a mobile station within a cellular telecommunications system, saidmethod comprising the steps of:maintaining, within a database of saidtelecommunications system, an activity flag associated with said mobilestation, said activity flag being set when said mobile station isactive; transmitting, by said mobile station, an identification signal aplurality of times while said mobile station is idle, wherein saididentification signal is transmitted by said idle mobile station atpseudo-randomly space intervals; varying the frequency of saidpseudo-random transmissions, by a control signal sent to said mobilestation, based on the areas in which said mobile station had beenrecently operating; determining, after at least one of saididentification signal transmissions, whether said activity flag for saididle mobile station is active; and generating an alarm signal if saidactivity flag for said idle mobile station is active.